1. Field of the Invention
The present invention relates to novel silicone-modified polyimide resins and to a method for preparing these resins. More specifically, the present invention relates to novel silicone-modified polyimide resins that exhibit an excellent heat resistance, adhesion and bonding ability. The resins are therefore useful as an electrical insulating material, coating material, and adhesive. The present invention also relates to a method for the preparation of these novel silicone-modified polyimide resins.
2. Background Information
Polyimide resins are known to be heat-resistant materials with excellent mechanical strength, chemical resistance, and electrical insulating performance, and are therefore employed as heat-resistant films, adhesives, coatings, molding resins, and encapsulating resins.
The excellent property profile of polyimide resins make them particularly useful as electrical and electronic materials in a wide range of applications. These applications include but are not limited to enamel-wire coating agents, films for copper-laminated printed circuit boards, insulating films and sheets, various types of insulating coating agents, alpha-ray shielding films, cloth impregnation agents, and adhesives.
A deficiency of polyimide resins is their poor adhesion to inorganic substrates such as glass, ceramics, and silicon wafers. Some of the methods already proposed for remedying this deficiency are: (i) preliminary treatment of the substrate with a silane coupling agent; (ii) combining a silane coupling agent with a solution of the polyamic acid precursor of the resin; and (iii) introducing an aminoalkyl-substituted silyl group into the molecule of the polyamic acid. This approach is described in Kobunshi, Volume 33, Number 11, pp. 830-834 (1984)).
The disadvantage of treating the substrate with a silane coupling agent in accordance with method (i) is that addition of this treatment step makes the entire coating process more complicated and therefore adversely affects the work flow of this process. While addition of silane coupling agent to the solution of the polyamic acid intermediate as described in method (ii) yields an improvement in adhesion, the presence of the silane substantially decreases the viscosity of the polyamic acid intermediate.
The introduction of substituted silyl groups into the polyamic acid intermediate in accordance with method (iii) does not achieve satisfactory adhesion because the substituted silyl group can be introduced only at the terminal positions of the polyamic acid. Finally, all three prior art methods require lengthy heating at temperatures of at least 200.degree. C. to achieve imidization of the polyamic acid.